1. Field of the Invention
The present invention relates to a pulse code modulation (PCM) time division multiplex (TDM) switching network in time-space-time structure comprising switch-through units which, being internested and released on a time basis, each operate a plurality of TDM transmission lines and TDM intermediate lines which connect the switch-through units to one another, and more particularly to such apparatus in which the switch-through units effect the time-wise and spatial allocation of time channels seized on incoming TDM lines to time channels seized on outgoing TDM lines by means of time slot conversion.
2. Description of the Prior Art
In a switching network of this type which is well known in the art, for example one may refer to the German published application No. 24 44 854, the aforementioned switch-through units form at least one two-stage operating network. An operating network of this kind can be arbitrarily extended by adding further switch-through units. In such a case, however, it is necessary to reclassify the TDM lines which connect the switch-through units of the first stage to the switch-through units of the second stage. Reclassification of this type can be avoided if the second stage of the operating network initially contains a number of switch-through units corresponding to the desired completed system. An extension can then be simply achieved by adding further switch-through units in the first stage without the necessity of reclassifying the TDM intermediate lines. However, as stated above, specific provisions must then be provided in the basis construction of the circuits. Furthermore, reclassification cannot be avoided when an extension is effected by adding further of the aforementioned operating networks. The TDM intermediate lines which, for example, establish connections between the particular second stages of two fully-developed operating networks must then, in fact, be used in part to establish connections to the added operating networks.